Need some help before tomorrow!!!!

hey guys i'm going to look at a friends setup tomorrow. he has 2 kicker cvx 12's 2 pioneer 800 mono drive amps eclipes deck and 2 1 fared capacitors hooked together with a bus bar. he had a friend hook it up for him and when he runs one amp only he says it hits really hard but when they split the rcas and run both amps it dies off and the rear speakers are louder than the subs. i'm thinking the rca in the radio are bad but i'm not sure. i haven't actually looked at it yet but just trying to get some help before i look at it tomorrow. does anyone have any ideas for what i can look for or what may be a problem. thanks in advance

he just left and i'm thinking one of his amps is bad. i hooked both subs to one and it was loud and then both to the other and just wasn't the same sound. so he's going to get another 1200w amp to try it.....

he only had one amp running one sub when he got here and i switched rca to the other amp and sub it just wasn't hitting as hard as the other. so i unhooked the wire from the other sub and ran both subs to the one amp i'm sure thats working good and it sounded pretty good when he left. he was going to buy a 1200 watt amp his friend had for $125. i don't know alot about the mono amps, i've never seen an amp with just one set of input rca's. whoever put it in for him did a sh*t job anyways so i'm trying to talk him into bringing it back to me and let me redo all the stuff thats "wire tied" together.............